To check if your Windows 7 is activated:-

Start - right click on computer - then on Properties - wait a few seconds and scroll to the bottom - it should tell you under Windows activation.

Here is a link to the Windows validation tool.

This comment appeared in a blog I was reading:-

"have you changed or upgraded any Hardware on your machine recently because if so then this would be why you have a message saying this copy of windows is not genuine if you have an OEM Machine. If it is OEM then what happens is the key is tied to the Hardware on that Manufacturer's computer hardware."

Try restoring your system to a time before the error message.

If the problem persists can I suggest that you ring the Microsoft Helpline here.

Or just activate again but use the phone option instead.

I agree with difarn. A few months ago a MS update caused a similar problem, only solved in the end by the MS team on the Phone.(They took control and sorted it. You need the activation code to hand.)

Did you read my link above?

If so and it failed to help, try the suggestion here titled "Most Helpful Reply".

Thanks for feedback - could you give a green tick? (on right side)